Camshaft phasers for varying the timing of combustion valves in an internal combustion engine transmit crankshaft torque to the engine camshaft, allowing varied timing of the camshaft relative to the crankshaft position. Traditionally, intake phasers have authority to only advance this timing from their locked position. When insufficient oil pressure is available for controlled phasing, cam torque and the available oil pressure are used to drive the rotor to the fully retarded position where a lock pin in the rotor aligns with a seat in the stator. As engine speed decreases, oil pressure drops below the retraction pressure for the lock pin and the pin's bias spring urges the pin to move into engagement with its seat, preventing undesired phase angle changes until sufficient oil pressure is again available.
Phasers requiring an intermediate lock pin position between full rotor advance and full rotor retard cannot rely on the contract between the rotor and stator to realign the lock pin to its seat. Therefore, when oil pressure is low, some form of assistance is needed to advance the rotor away from full retard to align the lock pin to the seat at the intermediate rotor position. If the assistance were torque from a simple spring-arm system, the bias spring would cause the phaser to advance the rotor through the entire range of rotor authority and past the point where the lock pin aligns with its seat when resistive torque through the phaser system from the camshaft was less than the applied spring torque.
What is needed in the art is an improved bias system for a modern phaser having a rotor lock position intermediate in the rotor range of authority wherein the rotor is biased toward the lock position from all retard positions but is not biased toward the lock position from any advance position.
It is a principal object of the present invention to provide an improved phaser bias system.